Telephone substation apparatus



Feb. 13, 1940. ,190,467

- F. HAMBURGER. NOW BY ,luL-zciAL CHANGE OF NAME FRAY HARDWICK TELEPHONESUBSTATION APPARATUS Filed Oct. 8, 1937 TELEPHONE C/RCU/T E LE C TR/CALC OUPL ING ACOUS T/C COUPL lNG lllillllxmlll-u'l t a I'll JHII -II 'IIIlNl/ENTOR By F. HAMBURGER 0 mm 6. ,KWL

AT TOR/W5) Patented Feb. 13, 1940 TELEPHONE SUBSTATION APPARATUS FreyHamburger, Orange, N. .12, now by judicial change of name Fray Hardwick,assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y.,a corporation of New York Application October 8, 1937, Serial No.167,904

7 Claims.

This invention relates to telephone substation apparatus and moreparticularly to telephone handsets.

Telephone handsets usually comprise a handle, a transmitter mounted ator adjacent one end of the handle and a receiver mounted at or adjacentthe other end of the handle. When the handset is used, the user may findit convenient or necessary during the course of a telephone conversationto place the handset upon a support, such, for example, as the top of adesk or table. When the handset is thus positioned, a relatively closeacoustic coupling is established between the diaphragms of thetransmitter and the receiver and an electro-acoustic circuit includingthe receiver and the transmitter is completed. This circuit may have anatural period Within the audio-frequency range so that when the handsetis placed upon the support the circuit resonates and an objectionablehowling is produced.

One object of this invention is to substantially prevent or minimize thehowling tendency in telephone handsets under certain conditions of use.

In accordance with one feature of this invention, the handle of thehandset is provided with one or more cavities having a restrictedorifice extending from the face of the handle nearest the transmitterand receiver. Each cavity and its associated orifice constitute anacoustic resonator which absorbs energy from the sound field between thediaphragms of the transmitter and receiver so that the acoustic couplingbetween the diaphragms is reduced. The resonator preferably is sodesigned that its natural frequency is substantially equal to or of theorder of the resonant frequency of the electro-acoustic system whenconditions are the most conducive to the production of the howling tone.7

The invention and the foregoing and other features thereof will beunderstood more clearly and fully from the following detaileddescription with reference to the accompanying drawing in which:

Fig. 1 is a view partly schematic and partly diagrammatic of telephoneapparatus, illustrating the couplings between the transmitter and thereceiver of the telephone handset;

Fig. 2 is a side view of a telephone handset constructed in accordancewith this invention, portions of the handle and of the transmitter andreceiver caps being broken away to show parts of the transmitter andreceiver and the resonators in the handle;

Fig. 3 is a front view of the handset shown in Fig. 2; and

Fig. 4 is an enlarged sectional view alongfline 4-4 of Fig. 3illustrating the configuration of the cavities in the handle of thehandset.

Referring now to the drawing, the telephone handset comprises a support,which maybe of molded insulating material, including a handle III, atransmitter portion II at one end of the handle and a receiver portionI2 at the other end of the handle, the portions I I and I2 havingcavities therein for accommodating a transmitter and a receiverrespectively. The transmitter and receiver may be of any of the usualtypes. For example, the transmitter may include a unit of the generalconstruction disclosed in Patent 2,042,822, granted June 2, 1936, toArthur F. Bennettand William L. Tuffnell and comprising a diaphragm I3and a carbon granule element I4. The transmitter unit may be held inplace, together with protective grills I5, by a centrally aperturedclamping member, cap or mouthpiece I6.

The receiver may include a unitof the general construction disclosed inthe application of Louis A. Morrison and Edward E. Mott, Serial No.93,792, filed August 1, 1936, and comprising an electromagnet element I1and a magnetic diaphragm I8 associated with the electromagnetic element.The receiver unit may be held on position in the portion I2 by aclamping member, cap or ear-piece I9 having a central grid portion 20.

As shown in Figs. 1 and 2, the clamping members or caps I6 and I9 areinclined toward each other.

When the handset is used, the transmitter and receiver are coupledelectrically to each other and a telephone line 2I by conductors 22, and23, the latter of which may be embedded in the handle I0. In the courseof a telephone conversation, the user may place the handset upon asupport 24, such for example as a shelf or the top of a desk or table,with the diaphragms I3 and I8 thereadjacent. Consequently, a confinedsound path is established between the diaphragms I3 and I8 and arelatively close acoustic coupling exists between the transmitter andreceiver. An electro-acoustic circuit is also completed including thetelephone line 2|, the transmitter and receiver and the acoustic pathbetween the diaphragms I3 and I8. This circuit may resonate at afrequency Within the audio-frequency range as a result of which a sharpsustained tone is produced and an objectionable howling or singingestablished.

In accordance with one feature of this invention, means are provided inthe handle of the handset for reducing the acoustic coupling between thetransmitter and the receiver under the aforesaid conditions of use, sothat the howling tendency is suppressed or minimized. In one form, thismeans comprises a plurality of chambers or cavities 25- and 26 in thehandle it, the chambers or cavities having communication with theatmosphere through restricted openings or orifices 21 and 28respectively in a plate member 29 seated in the inner substantially flatsurface of the handle and affixed thereto as by screws 33.

The chambers or cavities together with the orifices therefor constituteacoustic resonators which absorb energy from the sound field orrestricted sound path between the transmitter and receiver diaphragms.By thus absorbing energy, the resonators in eflfect introduce losses inthe electro-acoustic system which may be commensurate with the gains inthe circuit attributable to the transmitter and thereby prevent or atleast greatly reduce the pressures in the vicinity of the transmitterdiaphragm l3 occasioned by waves emanating from the receiver diaphragm I8. Consequently, the establishment of close acoustic coupling betweenthe transmitter and the receiver is prevented and the howling tendencyis suppressed.

The extent to which the resonators will absorb energy is dependent uponthe dimensions thereof which, of course, determine the natural frequencyof the resonators. The natural frequency may be ascertained from therelation to the length (L) thereof, and Vois the volume of the cavity.

Each of the resonators will absorb the most energy at frequenciescommensurate with the natural period thereof. Hence, preferably theresonators are designed so that each is resonant somewhat broadly atapproximately the frequency of the howling tone which would beproduced-when the handset is placed upon the support 24' with thediaphragms it and it in approximately face to face relation therewith.Inasmuch as the howling frequency may vary over some range dependingupon the character of the support 24 and the position of the diaphragmswith respect thereto, it is preferable that the resonators havedifferent natural frequencies within the range of howling frequenciesapt to be produced. For example, in a specific handset design it wasfound that when the handset was positioned upon a support as shown inFig. 2, the greatest tendency to howl occurred at about 2800 constitutedby the cavity 25 and orifice 27 to have-a natural frequency of about2400 cycles per second and the resonator ccnstitutedby the cavity 26 andorifice 28 to have a natural period of about 2800 cycles per second.

As-- disclosed in the copending application of Arthur F. Bennett, SerialNo. 167,894, filed Octoher. 8; 1937,. the receiver cap is may beprovided with a plurality of cavities 3t, 32 and 33 having orifices 34;35 and 36 respectively, which constitute resonators and absorb energyfrom the sound field between the receiver and the transmitter. Theseresonators may have natural periods of 2206, 2500 and 2800 cycles persecond respectively. In a handset having such resonators in the receivercap, or in the transmitter cap, preferably the resonators 25, 2? and 2t,28 should have natural periods different from those of the resonators inthe receiver or transmitter cap. For example, in a specific case Wherein the latter resonators had natural periods as set forth above, it wasfound satisfactory to have the resonators in the handle it resonate at1890 and 2000 cycles-per second.

Although in the specific embodiment of the invention shown anddescribed, two resonators are provided in the handle ill, it will beunderstood that a single resonator or more than two resonators may beprovided therein. Furthermore, it will be understood that. various othermodifications may be made in the telephone handset shown and describedwithout departing from the scope and spirit of this invention. asdefined in the appended claims. i

What is claimed is:

1. A telephone handset comprising a handle having an elongated surface,and a pair of telephone instrui'nents mounted on said handle adjacentopposite ends of said surface and'h'aving vibratile elements facing ingenerally the same direction with respect to said handle, said handlehaving a cavity therein with a resonant frequency within the range to betranslated by said instruments, said cavity being connected to theatmosphere through an opening in said surface facing the sound fieldbetween said instruments.

2. A telephone handset comprising a handle including a portion having asubstantially flat surface, a receiver and a transmitter. mounted inspaced relation on said handle and having diaphragms facingin-substantially the same direction as said surface, and an air chamberin said handle connected with the atmosphere through an opening in saidsurface, said chamber and opening being constructed and arranged toconstitute a resonator resonating at a preassigned frequency.

3; A telephone handset comprising a support including a handle,telephone instruments mounted in spaced relation on said support,resonant means in said handset adjacent one of said instruments, andvother resonant means in said handle, said first and second means havingnatural periods within the range of frequencies to be translated by saidtelephone instruments and being acoustically coupled to the sound fielddirectly between said instruments.

4.11 telephone handset in accordance with claim 3 wherein said first andsaid second resonant means have different natural periods.

5. A telephone handset comprising a support including a. handle, atransmitter at one end. of said handle, a receiver at the other end of;said handie, a plurality of resonators in said: handset' adjacent saidreceiver, said resonators having different resonant frequencies, and ap1u.- rality of resonators in said handle having resonantfrequenciesdifierent from the resonant frequency of said firstresonators.

ii. A telephone handsetv comprising a handle, a transmitter at one endof said handle, a receiver at the other endof said handle, a pluralityof cavities in said handle intermediate the ends thereof; and-a platemember overlying'said cavities and having a plurality of restrictedopen- 1 ings each in communication with one of said between saidreceiver and said transmitter, said cavities and the sound fielddirectly between saidcavity and orifice constituting a resonator havingtransmitter and receiver. a a natural frequency of the order of thefrequency 7. A telephone handset comprising a handle, a at which saidhandset tends to howl when placed transmitter at one end of said handle,a receiver upon a surface with said transmitter and said 5 at the otherend of said handle, said receiver and receiver in substantially face toface relation said transmitter being inclined toward each therewith.other, and a cavity in said handle having an FREY HAMBURGER. orifice incommunication with the sound field

